Process for de-airing material in an extruder that includes a vent block

ABSTRACT

An extruder for feeding material and for removing gas from the fed material. The extruder includes a vent block positioned between a first and second auger. The vent block including a vent cavity having a feed end and an exit end, an inner feed ring that partially extends into said vent cavity at the feed end of the vent cavity, and a screw element rotatably positioned in the vent cavity. A front portion of the outer ring is longitudinally aligned with or overlapping the front end of the inner feed ring. The outer ring forms at least one gap or opening at or adjacent the feed end of the vent cavity to enable gas to flow out of the vent cavity as material is moved though the vent cavity from the feed end to the exit end by the screw element.

The present invention claims priority on U.S. Provisional ApplicationSer. No. 61/418,631 filed Dec. 1, 2010, which is fully incorporatedherein by reference.

The present invention is a device used to remove gas and/or moisturefrom a material being process by an extruder.

BACKGROUND OF THE INVENTION

Many types of materials that are processed in an extruder can includeentrapped air and/or other types of gasses. The entrapped air and/orother types of gasses can interfere with the proper processing of thematerials in the extruder. Various arrangements have been developed toremove air and/or other types of gasses during the processing ofmaterials in the extruder. Non-limiting examples of such arrangementsare disclosed in U.S. Pat. Nos. 2,833,750; 2,944,047; 3,040,005;3,156,009; 3,177,272; 3,799,234; 3,870,284; 3,985,348; 4,065,532;4,100,244; 4,127,635; and 4,155,655, all of which are incorporatedherein by reference.

Many prior art extruder systems that include a venting arrangement areused to extrude polymer materials. Polymer materials, when beingextruded through the extruder, are generally in a fluid form thatenables the polymer to easily flow through the extruder. Typically anopening is formed in the barrel of the extruder and gas (e.g., air,nitrogen, water vapor, etc.) is removed from extruder as the polymer ismoved through the extruder. A diverter is commonly placed at or near theopening in the barrel to inhibit or prevent the polymer from flowinginto the opening and plugging the opening.

It has been found that materials that are more viscous than polymers ormaterials that are not true liquids, such as clays, mastics, ceramicsand the like have a tendency to plug the opening in the barrel even whena diverter is used. A true liquid material is defined as a material thatcannot resist shear and seeks a uniform level when placed in acontainer. As such, standard extruder arrangements that include aventing system cannot be used with highly viscous materials or non-trueliquid materials. Such materials can resist shear when being fed throughan extruder arrangement and building up on and eventually clog or plugthe opening in the barrel.

In view of the current state of the art of extruders, there is a needfor an extruder arrangement that can be used to remove gas from theextruder when extruding various types of materials, and especiallyhighly viscous materials or non-true liquid materials.

SUMMARY OF THE INVENTION

The present invention is directed to an improved extruder arrangementthat overcomes the past problems associated with prior art extrudersthat have openings in the barrel to remove air and/or other types ofgasses from the material as it is being fed through the extruder. Theimproved extruder arrangement of the present is particularly useful inextruding highly viscous and dense materials and/or non-true liquidmaterials (e.g., clays, ceramics, etc.) that gas to be removed from thehighly viscous and dense materials and/or non-true liquids as suchmaterials are being fed through the extruder arrangement and will bedescribed with particular reference thereto; however, it will beappreciated that less viscose material and/or true liquids can beextruded through the improved extruder arrangement. The removal ofgasses from the extruder arrangement of the present can be by use of avacuum pulled on the extruder arrangement; however, this is notrequired. As defined herein, a highly viscous material is a materialthat has a viscosity of 20,000 cP or greater at 25° C. The extrudergenerally includes an auger or screw that is rotated in a cavity that isformed by a cylinder or one or more barrels. The cross-sectional shapeof the cavity is generally circular or oval; however, the cavity canhave other cross-sectional shapes. The auger or screw includes a rootand one or more flights on the outer surface of the root. The root canbe partially or fully hollow, or can be solid. The flight height andflight angle on the screw is non-limiting. The diameter of the root ofthe anger or screw is non-limiting. The length of the auger or screw isnon-limiting. The pitch of the one or more flights on the auger or screwis non-limiting. Many different auger or screw configurations can beused on the improved extruder arrangement of the present invention.Examples of some non-limiting screw configurations are disclosed in U.S.Pat. Nos. 3,870,284; 3,989,941; 4,129,386; and 4,321,229, which areincorporated herein by reference. One or more motor and gear boxes canbe used to control the rotational speed of the auger or screw. A feedbox can be optionally used to feed material to the auger or screw;however, this is not required. Generally the auger or screw is fed withmaterial at the beginning or at the first stage of the auger or screw;however, one or more materials can be alternatively or additionally fedat other locations along the auger or screw (e.g., second state, thirdstate, etc.). A cooling system (e.g., cooling fluid, etc.) and/orheating system (e.g., warm or hot fluid, heating coils, heating jacket,etc.) can be used to heat and/or cool the material being fed through theextruder; however, this is not required. The cooling system and/orheating system, when used, can be positioned at one or more positionsalong the length of the extruder. The extruder can include a die plateand die plate holder system; however, this is not required. The dieplate, when used, is used to form specifically shaped extrusions;however, this is not required. The die plate, when used, can include oneor more openings. The one or more openings in the die plate canoptionally include one or more interests; however, this is not required.

In one non-limiting aspect of the invention, the improved extruderarrangement of the present invention includes a novel vent block that isused to draw gas such as, but not limited to, air from a material as thematerial is being feed through the extruder. The extruder can includeone or more vent blocks positioned along the length of the auger orscrew. Generally one vent block is positioned between the first andsecond stage of the extruder; however, this is not required. As can beappreciated, the vent block can be positioned is other or alternativelocations (e.g., between second and third stage of extruder, in firststage of extruder, in second stage of extruder, in third stage ofextruder, etc.). The different stages include the feeding stage (firststage), a transition stage (second stage), metering stage (third stage),and mixing stage (forth stage). The vent block is not limited in shape,size, or length. The components of the vent block are generally formedof durable materials (e.g., metal, plastic, composite materials,ceramic, etc.). The various components of the vent block can be formedof the same or different materials. The vent block includes a feedarrangement that enables material to be fed into a vent cavity andenables a vacuum to be pulled at a vacuum section that is located at oradjacent to the feed arrangement while minimizing or preventing materialform flowing into the vacuum section. The vacuum section and feedarrangement used in the vent block enables highly viscous materials,non-true liquid material, non-highly viscous materials and true liquidmaterials to flow through the vent block while a vacuum is pulled on thematerials passing through the vent block. As can be appreciated, gas canbe removed from the highly viscous materials, non-true liquid material,non-highly viscous materials and/or true liquid materials flowingthrough the vent block without having a vacuum being pulled on the ventblock. In one non-limiting embodiment of the invention, the feedarrangement includes an inner feed ring that extends into the ventcavity of the vent block from the feed wall of the vent block. The innerfeed ring is generally connected to or integrally formed with the feedwall of the vent block; however, this is not required. As can beappreciated, the one or more portions of the inner feed ring can beconnected to other or additional components of the vent block (e.g.,side walls, top wall, bottom wall, outer ring, etc.); however, this isnot required. The inner feed ring can be formed of one or more piece.The cross-sectional size and cross-sectional shape of the inner feedring are generally the same as or similar to the cavity of the barrel orfeeder section that is connected to the vent block and causes materialto be moved toward or into the vent block; however, this is notrequired. For example, if the vent block was connected after the firststage of the extruder, then cross-sectional size and cross-sectionalshape of the opening at the end of the barrel or formed by a pluralityof barrels are the same or similar to the cross-sectional size andcross-sectional shape of the inner feed ring of the vent block. Thecross-sectional size and/or cross-sectional shape of the inner feed ringcan be constant or change (e.g., increase, decrease, circular to oval,oval to circular, circular to polygonal, oval to polygonal, etc.) alongthe longitudinal length of the inner feed ring. The amount that theinner feed ring extends into the vent cavity is non-limiting. Generally,the inner feed ring extends no more than about 50% the totallongitudinal length of the vent cavity, typically no more than about 25%the total longitudinal length of the vent cavity, more typically no morethan about 25% the total longitudinal length of the vent cavity, stilltypically no more than about 15% the total longitudinal length of thevent cavity, and still more typically no more than about 12% the totallongitudinal length of the vent cavity. In another and/or alternativenon-limiting embodiment of the invention, the vacuum section is at leastpartially formed by an outer ring; however, this is not required. In onenon-limiting configuration, the outer ring defines all or a majority ofthe inner surface vent cavity. The outer ring can be formed of one ormore pieces. The cross-sectional size and/or cross-sectional shape ofthe outer ring can be constant or change (e.g., increase, decrease,circular to oval, oval to circular, circular to polygonal, oval topolygonal, etc.) along the longitudinal length of the outer ring. Assuch, the vent cavity that is fully or partially defined by the innersurface of the outer ring can have a constant or variablecross-sectional size and/or cross-sectional shape along the longitudinallength of the vent cavity. The outer ring is generally connected to theexit wall of the vent block; however, this is not required. The outerring can also to alternatively be connected to the feed wall of the ventblock; however, this is not required. As can be appreciated, the one ormore portions of the outer ring can be connected to other or additionalcomponents of the vent block (e.g., side walls, top wall, bottom wall,etc.); however, this is not required. The outer ring generally extendsabout 70-100% of the length between the exit wall and feed wall of thevent block, typically extends about 80-100% of the length between theexit wall and feed wall of the vent block, more typically extends about85-100% of the length between the exit wall and feed wall of the ventblock, even more typically extends about 90-100% of the length betweenthe exit wall and feed wall of the vent block, and still even moretypically extends about 94-100% of the length between the exit wall andfeed wall of the vent block. The outer ring includes one or moreopenings and/or forms one or more opening with the feed wall of the ventblock to enable gas to be drawn out of the vent cavity of the ventblock. In one non-limiting designed, one or more portions of the outerring are spaced from the feed wall of the vent block to form one or moregas gaps between the one or more portions of the outer ring and the feedwall. In one non-limiting arrangement, the complete outer ring is spacedfrom the feed wall. In another non-limiting arrangement, a portion ofthe outer ring is spaced from the feed wall and a portion of the outerring contacts the feed wall, connects to the feed wall and/or isinterconnected to the feed wall. In still another non-limitingarrangement, when all or a portion of the outer ring is spaced from thefeed wall, the spacing of the outer ring from the feed wall is less thanor equal to the distance that the inner feed ring extends from the feedwall and into the vent cavity. In such an arrangement, the end of theouter ring that forms that gap with the feed wall either is angled withthe end of the inner feed ring or overlaps the inner feed ring.Generally, the end of the outer ring that forms that gap with the feedwall overlaps about 1-99% of the inner feed ring, typically overlapsabout 10-99% of the inner feed ring, more typically overlaps about20-95% of the inner feed ring, still more typically overlaps about25-95% of the inner feed ring, even more typically overlaps about 30-95%of the inner feed ring, still even more typically overlaps about 50-95%of the inner feed ring, and yet even more typically overlaps about50-95% of the inner feed ring. In still yet another non-limitingarrangement, when the outer ring contacts the feed wall, connects to thefeed wall and/or is interconnected to the feed wall and includes one ormore openings in the outer ring for removal of gas from the vent cavity,the one or more openings either are aligned with the end of the innerfeed ring or overlaps the inner feed ring. Generally, the one or moreopenings in the outer ring overlap about 1-99% of the inner feed ring,typically overlaps about 10-99% of the inner feed ring, more typicallyoverlaps about 20-95% of the inner feed ring, still more typicallyoverlaps about 25-95% of the inner feed ring, even more typicallyoverlaps about 30-95% of the inner feed ring, still even more typicallyoverlaps about 50-95% of the inner feed ring, and yet even moretypically overlaps about 50-95% of the inner feed ring.

In still another and/or alternative non-limiting aspect of theinvention, the improved extruder arrangement of the present inventionincludes a novel vent block that has a specially configured screwelement designed to rotate within the vent cavity of the vent block. Thescrew element includes a root portion and one or more flights that areconnected to the outer surface of the root portion. The root portion canbe partially or fully hollow, or can be solid. The flight height and/orflight angle on the screw element are non-limiting. The diameter of theroot portion of the screw element is non-limiting. The cross-sectionalsize and/or shape of the root portion can be constant or can vary alongthe longitudinal length of the screw element. The flight height, flightangle and/or pitch of the one or more flights on the screw element canbe constant or can vary along the longitudinal length of the screwelement. The length of the screw element is generally the same length asthe vent cavity of the vent block; however, it can be appreciated thatthe screw element can be longer than or shorter than the length of thevent cavity. In one non-limiting embodiment, the screw element caninclude an auger connection arrangement on one or both ends of the screwelement; however, this is not required. The auger connectionarrangement, when used, is configured to connect one or both ends of thescrew element to an auger or screw of the extruder. The configuration ofthe auger connection arrangement is non-limiting. When an augerconnection arrangement is used on both ends of the screw element, theauger connection arrangements can be the same or different. In onenon-limiting configuration, at least a portion of the end of the rootportion is hollow and includes one or more key structures (e.g., slot,grooves, etc.) to engage and align one or both ends of the screw elementwith the end of an auger or screw. In another and/or alternativenon-limiting embodiment of the invention, the screw element includes oneor more fingers; however, this is not required. The one or more fingers,when used, are generally connected to a portion of one or more flightson the screw element; however, it can be appreciated that one or morefingers can also or alternatively be connected to the root portion ofthe screw element. In one non-limiting configuration, the one or morefingers are positioned at or near the feed end of the screw element sothat the one or more fingers can be designed to fully or partially clearmaterial from a region wherein the inner feed ring and outer ring of thevent block are aligned and/or overlap one another; however, this is notrequired. Such a configuration of the one or more fingers can be used toclear material from the region wherein the inner feed ring and outerring of the vent block are aligned and/or overlap one another so as tofacilitate in clearing the one or more gas gaps or gas openings that areused to remove gas from the vent cavity. When the inner feed ring andouter ring overlap one another, the front end of one or more of thefingers is designed to be positioned at least partially between theinner feed ring and outer ring and to move within such space as thescrew element rotates in the vent cavity; however, this is not required.Also, when the inner feed ring and outer ring overlap one another, thefront end of one or more of the fingers is designed to be positioned atleast partially between the inner feed ring and outer ring andpositioned to pass adjacent to or partially or fully over the one ormore gaps or openings and to move within the space between the innerfeed ring and outer ring as the screw element rotates in the ventcavity; however, this is not required. Generally, the one or morefingers are positioned in about 1-100% of the longitudinal length of theoverlay between the inner feed ring and outer ring, typically about25-100% of the longitudinal length of the overlay between the inner feedring and outer ring, more typically about 50-100% of the longitudinallength of the overlay between the inner feed ring and outer ring, andstill more typically about 75-100% of the longitudinal length of theoverlay between the inner feed ring and outer ring. Also oralternatively, the one or more fingers are generally positioned overabout 1-100% of the longitudinal length of the gap or opening used tovent gas from the vent cavity, typically positioned over about 10-100%of the longitudinal length of the gap or opening used to vent gas fromthe vent cavity, more typically positioned over about 25-100% of thelongitudinal length of the gap or opening used to vent gas from the ventcavity, still more typically positioned over about 40-100% of thelongitudinal length of the gap or opening used to vent gas from the ventcavity, and even more typically positioned over about 50-100% of thelongitudinal length of the gap or opening used to vent gas from the ventcavity. In another and/or alternative non-limiting configuration, thefront of one or more fingers can be tapered or otherwise configured tocause material to be moved away from and/or out between the gap betweenthe inner feed ring and outer ring; however, this is not required.

In yet another and/or alternative non-limiting aspect of the invention,the improved extruder arrangement of the present invention includes avent block that has a vent cavity and/or screw element that are designedto cause a pressure drop as material is fed into the vent cavity;however, this is not required. The pressure drop is designed to limit orprevent material from flowing into the one or more gaps or openings inthe vent cavity that are used to pull a vacuum on the vent cavity. Thecreation of a pressure drop can be achieved in one or more ways, suchas, but not limited to, 1) creating a portion of the vent cavity havinga larger cross-sectional size to the cross-sectional size of the openingin the inner feed ring, 2) reducing the root portion of the screwelement as compared to the root of the auger or screw feeding materialinto the vent block, and/or 3) increasing the pitch of the one or moreflights on the screw element as compared to the flight pitch of theauger or screw feeding material into the vent block.

In still yet another and/or alternative non-limiting aspect of theinvention, the improved extruder arrangement of the present inventionincludes a vent block that includes one or more viewing windows toenable a user to view the interior of the vent cavity to determinewhether one or more gaps or openings used to vent gas from the ventcavity are clear or plugged; however, this is not required.

In another and/or alternative non-limiting aspect of the invention, theimproved extruder arrangement of the present invention includes a ventblock that includes one or more doors that enable a user to access thevent cavity and/or interior of the vent block; however, this is notrequired. The one or more doors can include a sealing arrangement (e.g.,sealing strip, sealing ring, etc.) to form a partial or full air tightseal with the door frame when the door is closed; however, this is notrequired.

It is one non-limiting object of the present invention to provide anextruder arrangement that can remove gas from material that is being fedthrough the extruder.

It is another and/or alternative non-limiting object of the presentinvention to provide an extruder arrangement that includes a vent blockthat is used to remove gas from material that is being fed through theextruder.

It is still another and/or alternative non-limiting object of thepresent invention to provide an extruder arrangement that includes avent block having an inner feed ring and an outer ring and which ringsare used to enable gas to be removed from a vent cavity while materialis fed through the vent cavity and to inhibit or prevent material frommoving into and/or clogging one or more gaps or openings that are usedto remove gas from the vent cavity.

It is yet another and/or alternative non-limiting object of the presentinvention to provide an extruder arrangement that includes a vent blockthat includes a screw element having one or more fingers that are usedto inhibit or prevent material from moving into and/or clogging one ormore gaps or openings that are used to remove gas from the vent cavity.

It is still yet another and/or alternative non-limiting object of thepresent invention to provide an extruder arrangement that includes avent block that includes one or more viewing windows to enable a user todetermine whether one or more gaps or openings that are used to removegas from the vent cavity are clogged or unclogged.

These and other objects and advantages will become apparent to thoseskilled in the art upon reading and following the description takentogether with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference may now be made to the drawings which illustrate variouspreferred embodiments that the invention may take in physical form andin certain parts and arrangement of parts wherein:

FIG. 1 is a side elevation view of an extruder arrangement in accordancewith the present invention;

FIG. 2 is an enlarged side elevation view of a portion of the extruderarrangement of FIG. 1 showing the vent block connected between the firstand second stage of the extruder;

FIG. 3 is a side sectional view of the vent block;

FIG. 4 is a side elevation view of a screw element that is positioned inthe vent block; and,

FIG. 5 is side sectional view of an alternative configuration of thevent block.

DETAILED DESCRIPTION OF ONE NON-LIMITING EMBODIMENTS

Referring now to the drawings wherein the showings are for the purposeof illustrating one non-limiting embodiment of the invention only andnot for the purpose of limiting same, FIGS. 1-4 illustrate onenon-limiting embodiment of the extruder arrangement in accordance withthe present invention. The extruder arrangement 10 is designed to removeone or more gasses (e.g., air, nitrogen, water vapor, volatiles, etc.)from the material being feed through the extruder arrangement. The oneor more gasses can create gas bubbles in the final product and/orinterfere with the proper extrusion of the final product, thuscompromising the integrity and/or quality of the final product extrudedfrom the extruder arrangement. The extruder arrangement 10 isparticularly useful in the extrusion of highly viscous materials and/ornon-true liquids (e.g., clay materials, ceramic materials, etc.) andwill be described with particular reference thereto; however, it will beappreciated that materials that are not highly viscous and/or trueliquids can also be extruded through the extruder arrangement of thepresent invention. Highly viscous materials and/or non-true liquids thatrequire gas to be removed from the highly viscous material and/ornon-true liquids during extrusion pose special that do not exist fornon-highly viscous materials or true liquid materials. Specially,traditional openings for removing gasses used in the barrels cannot beused to draw gas from highly viscous material and/or non-true liquidsduring the extrusion process. Highly viscous material and/or non-trueliquids resist shear as the material is fed through the extruderarrangement. Such resistance to shear results in the material buildingup around the opening in the barrel and ultimately plugging or cloggingthe opening. The extruder arrangement of the present invention overcomesthese short comings of past extruder configurations by the use of anovel vent block 100 that is positioned in one or more locations alongthe extruder arrangement. FIG. 1 illustrates that only a single ventblock is used in the extruder arrangement, however, it can beappreciated that more than one vent block can be used in to extruderarrangement. As will be described in more detail below, the novel ventblock of the present invention is designed to remove gas from highlyviscous material and/or non-true liquids being fed through the extruderarrangement while overcoming past problems associated with the pluggingor clogging of the one or more openings used to remove gas from thehighly viscous material and/or non-true liquids as it moves through theextruder arrangement.

Referring again to FIG. 1, the extruder arrangement 10 includes amaterial feeder or chute 20 used to feed material into the extruderarrangement. The feeder 20 includes an opening 22 designed to receivematerial such as a highly viscous material (e.g., clay material, etc.)as indicated by the arrow. The use of a material feeder is not required.The size and configuration of the material feeder is non-limiting. Thematerial used to form the material feeder is also non-limiting.

Once a material is fed into the material feeder, the material contactsthe front end portion of a first auger 30. The first auger includes acentral root portion 32 and one or more flights 34 connected to theoutside surface of the root portion. The tight 34 has a helicalconfiguration and is designed to move material in the material feederout of the material feed through a feeder exit opening 24 and into afirst barrel section 40. The first auger is generally rotated clockwiseby a motor M as indicated by the arrow; however, it can be appreciatedthat the first auger can be rotated counterclockwise. A gear box, notshown, can be used in conjunction with the motor to control the speed ofrotation of the first auger; however, this is not required. The diameterof the root portion of the first auger is non-limiting. The diameter orthe root portion can remain constant or vary along the longitudinallength of the first auger. The height and/or pitch of the one or moreflights on the auger can remain constant or vary along the longitudinallength of the first auger. The first auger can include one or moreflight breaks along the longitudinal length of the first auger; however,this is not required.

First barrel 40 can be formed of one or more parts. Typically, the firstbarrel is formed of two halves that are bolted or otherwise connectedtogether. The material used to form the first barrel is non-limiting.The first barrel includes a first flange 42 that is connected by bolts44 or some other or additional connection arrangement (e.g., threadedconnection, rivet, adhesive, etc.) to the material feeder. Although notshown, the first barrel can optionally include a heating and/or coolingjacket and/or coils to heat and/or cool the material moving though thefirst barrel. The cross-sectional size and cross-sectional shape of thecavity 46 formed by the first barrel can be constant or vary along thelongitudinal length of the first barrel. The longitudinal length of thefirst barrel is non-limiting. The first barrel line can be designed toenable two or more augers to rotate within the cavity of the firstbarrel; however, this is not required. As illustrated in FIG. 1, thecross-sectional size and circular cross-sectional shape of the cavityformed by the first barrel is generally constant along the longitudinallength of the first barrel. Referring now to FIGS. 1-3, a second flange48 on the first barrel is connected to the vent block 100 by bolts orsome other or additional connection arrangement. As best illustrated inFIG. 3, a bolt 120 is used to secure the first barrel to the feed wallof the vent block. The head of bolt 120 is illustrated as positioned ina bolt head recess 122 on the inner surface 116 of the feed wall;however, this is not required. The body of bolt 120 passes through abolt opening 124 and is secured to second flange 48 on the first barrel.As can be appreciated, other or additional arrangements can be used tosecure the first barrel to the vent block. As illustrated in FIG. 3, thehead of bolt 122 passes partially or fully through an opening 138 in theinner feed ring; however, this is not required. As can be appreciated,the inner feed ring can be designed so that bolt 122 partially or fullysecures the inner feed ring to the inner surface 116 of the feed wall ofthe vent block; however, this is not required.

The vent block 100 is illustrated as having a generally cubical shape;however, this is not required. The materials used to form the componentsof the vent block are non-limiting (e.g., metal, plastic, compositematerials, glass, ceramic, etc.). As illustrated in FIGS. 2 and 3, thefirst barrel liner is connected to the feed wall 110 of the vent block.The outer surface 112 of the feed wall can optionally include a flangerecess 114 to receive a portion of second flange 48 on the first barrelliner. The feed wall includes a feed opening 117 to enable the ventblock to be in fluid communication with the cavity of the first barrelliner so that material can be fed into the vent block from the firstbarrel liner as the first auger rotates in the cavity of the firstbarrel liner. The rear end 36 of the first auger is illustrated aspassing partially or fully through the feed wall and engaging andconnecting to a front end 310 of screw element 300 in the vent block. Ascan be appreciated, the front end of screw element 300 can alternativelyextend partially or fully through the feed wall and engage and connectto the rear end of the first auger. The rear end of the first auger isillustrated as tapered so as to reduce the cross-sectional size of theroot portion 32 to match or closely match the cross-sectional size ofthe root portion 320 of the screw element; however, this is notrequired. The taper, when used, can be at a constant or variable angle.A portion or all of root portion 320 can include a cavity 322 asillustrated in FIG. 4; however, this is not required. When a cavity 322is present at least in the front portion of the screw element, thecavity can be designed to telescopically receive a rear portion of thefirst auger when the first auger is connected to the screw element;however, this is not required. The cavity located in the front portionof the screw element, when used, can optionally include a keyarrangement 324 that is designed to align and/or lock the screw elementin rotational alignment with the first auger so that the first auger andscrew element rotate together; however, this is not required. The keyarrangement can also or alternatively be used to secure the screwelement to the first auger; however, this is not required. Keyarrangement 324 is illustrated as in the form of a slot or recess;however, it can be appreciated that other or additional structures canbe used.

An inner feed ring 130 is connected to the inner surface 116 of the feedwall of the vent block. The inner feed ring can be formed of one or morepieces. Bolt 132 is illustrated as passing through a bolt opening 134 inthe inner feed ring and into a bolt opening 118 in the inner surface ofthe feed wall. The one or more bolts 132 are used to secure the innerfeed ring to the inner surface of the feed wall. As can be appreciated,other or additional connection arrangements can be used to secure theinner feed ring to the inner surface of the feed wall (e.g., rivet,adhesive, weld bead, solder, etc.). As can also be appreciated, theinner feed ring can be partially or fully formed in the feed wall;however, this is not required. The inner feed ring includes a feedflange 138 that extends into the vent cavity 150 of the vent block. Thefeed flange is designed to only partially extend into the vent cavity.Generally, the feed flange extends into the vent cavity at least about0.1% of the total longitudinal length of the vent cavity, typically thefeed flange extends into the vent cavity at least about 0.5% of thetotal longitudinal length of the vent cavity, more typically the feedflange extends into the vent cavity at least about 1% of the totallongitudinal length of the vent cavity, still more typically the feedflange extends into the vent cavity at least about 2% of the totallongitudinal length of the vent cavity, even more typically the feedflange extends into the vent cavity at least about 5% of the totallongitudinal length of the vent cavity, and yet even more typically thefeed flange extends into the vent cavity at least about 7% of the totallongitudinal length of the vent cavity. Also, the feed flange generallyextends into the vent cavity no more than about 50% of the totallongitudinal length of the vent cavity, typically the feed flangeextends into the vent cavity no more than about 30% of the totallongitudinal length of the vent cavity, more typically the feed flangeextends into the vent cavity no more than about 25% of the totallongitudinal length of the vent cavity, still more typically the feedflange extends into the vent cavity no more than about 20% of the totallongitudinal length of the vent cavity, and even more typically the feedflange extends into the vent cavity no more than about 15% of the totallongitudinal length of the vent cavity. The feed flange generally formsan opening 140 that is the same cross-sectional shape and size as theopening 136 in the front end of the feed ring, and is centrally alignedwith the central axis of opening 136; however, this is not required. Ascan be appreciated, the feed flange can be tapered to reduce or enlargethe cross-section size of opening 140 relative to opening 136; however,this is not required.

Cavity 150 of the vent block is partially or fully formed by an outerring 160. The outer ring can be formed of one or more pieces. The secondend 162 of the outer ring is illustrated as connected to the innersurface 182 of exit wall 180; however, this is not required. As can beappreciated, the outer ring can also or alternatively be connected tofeed wall 110. As illustrated in FIG. 3, second end of the outer ringincludes a mount flange 164 that includes a bolt opening 166. A body ofa bolt 170 is illustrated as passing through bolt opening 166 andconnecting in an opening 184 of exit wall 180. As can be appreciated,other or additional arrangements can be used to connect the outer ringto the inner surface 182 of the exit wall (e.g., weld bead, solder,rivet, adhesive, etc.). As can be appreciated, the outer ring can bepartially or fully formed on the outer wall; however, this is notrequired.

The cavity 150 of the vent block can have a constant or variablecross-sectional shape and cross-sectional size along the longitudinallength of the vent cavity. As illustrated in FIG. 3, the cross-sectionalshape of the vent cavity is generally circular and remains generallyconstant along the longitudinal length of the vent cavity and thecross-sectional size of the vent cavity varies along the longitudinallength of the vent cavity. The cross-sectional size of the front portion152 of the vent cavity at the feed wall of the vent block is illustratedas larger than the cross-sectional size of the end portion 156 of thevent cavity at the exit wall of the vent block. The cross-sectional sizeof the vent cavity can vary at a constant rate along the length of thevent cavity; however, this is not required. As illustrated in FIG. 3,the cross-sectional size of the vent cavity from the feed wall to morethan 50% the longitudinal length of the vent cavity remains generallyconstant. Thereafter, the vent cavity tapers down at a taper portion 154to a smaller cross-sectional size and then remains a constant small sizefor a short distance to the exit wall. As can be appreciated, manydifferent vent cavity configurations can be used in the vent block. Asillustrated in FIG. 5, the cross-sectional shape and cross-sectionalsize of the vent cavity is generally constant along the longitudinallength of the vent cavity.

Referring again to FIG. 3, the outer ring 160 has a first end 168 thatis illustrated as spaced from the inner surface 116 of the feed wall.All or a portion of the first end can be spaced from the inner surfaceof the feed wall and/or the inner feed ring. In one arrangement, thecomplete first end of the outer ring is spaced from the inner surface ofthe feed wall and/or inner feed ring. In such an arrangement, the outerring is fully supported on the inner surface of the exit wall. As can beappreciated, the outer ring could also or alternatively be supported onother wall of the vent block (e.g., top wall, bottom wall, side wall,etc.). In another arrangement, a portion of the first end of the outerring is spaced from the inner surface of the feed wall and a portion ofthe first end contacts the inner surface of the feed wall and/or innerfeed ring. In such an arrangement, a portion of the first end can besupported by, connected to and/or interconnected to the feed wall and/orinner feed ring; however, this is not required. The cavity gap 190 thatis formed between the front end of the outer ring and the inner surfaceof the feed wall and/or inner feed ring is used to withdraw gas from thevent cavity as material is fed through the vent cavity. The size and/orshape of the space or gap 190 is non-limiting. As can be appreciated,the front portion of the outer ring can include one or more openingsthat can also or alternatively be used to withdraw gas from the ventcavity as material is fed through the vent cavity; however, this is notrequired. As illustrated in FIG. 3, the first end of the outer ring isspaced from the inner feed ring to form cavity gap 190.

As illustrated in FIG. 3, the first end of the outer ring extends overthe feed flange 138 of the feed ring so as to cause an overlaparrangement between the inner feed ring and outer ring. The overlappingportion of the two rings forms a ring gap 192. The ring gap 192 inconjunction with the cavity gap 190 forms a gas path that enables gas tobe withdrawn from the vent cavity. The width of the ring gap isgenerally constant; however, this is not required. The front end portionof the outer ring generally extends over or overlap about 0.1-99% of thelongitudinal length of feed flange 138, typically, the front end portionof the outer ring generally extends over or overlap about 1-95% of thelongitudinal length of feed flange 138, more typically the front endportion of the outer ring generally extends over or overlap about 5-95%of the longitudinal length of feed flange 138, still more typically thefront end portion of the outer ring generally extends over or overlapsabout 10-95% of the longitudinal length of feed flange 138, even moretypically the front end portion of the outer ring generally extends overor overlaps about 20-95% of the longitudinal length of feed flange 138,yet even more typically the front end portion of the outer ringgenerally extends over or overlaps about 25-95% of the longitudinallength of feed flange 138, yet still even more typically the front endportion of the outer ring generally extends over or overlaps about30-95% of the longitudinal length of feed flange 138, even moretypically the front end portion of the outer ring generally extends overor overlaps about 40-95% of the longitudinal length of feed flange 138,still more typically, the front end portion of the outer ring generallyextends over or overlaps about 50-95% of the longitudinal length of feedflange 138, yet more typically the front end portion of the outer ringgenerally extends over or overlaps about 60-95% of the longitudinallength of feed flange 138, still more typically the front end portion ofthe outer ring generally extends over or overlaps about 60-90% of thelongitudinal length of feed flange 138, and still yet even moretypically the front end portion of the outer ring generally extends overor overlaps about 60-80% of the longitudinal length of feed flange 138.

As illustrated by the arrows in FIG. 3, gas is drawn out of the ventcavity thought ring gap 192, then through cavity gap 190 and into anouter chamber 250 of the vent block. The outer chamber fully orpartially encircles and encompasses the vent cavity and outer ring. Asillustrated in FIG. 3, the bottom wall 260 of the vent block includes avacuum opening 262 that is used to draw gas from the outer chamber. Agas line 264 is connected to the vacuum opening and is generallyconnected to a vacuum pump, not shown, to draw a vacuum on the ventcavity. As can be appreciated, more than one vacuum opening can bepositioned in the bottom wall. As also can be appreciated, one or morevacuum openings can also or alternatively be positioned in the top wall270 and/or one or more side wall; however, this is not required. As canfurther be appreciated, a vacuum is not required to be pulled on any ofthe vacuum openings 262, thus enabling gas to exit the vent blockwithout use of a vacuum being pulled on the vent block. As can beappreciated, the top and bottom walls can be connected to the feed andexit walls in any number os ways (e.g., weld bead, solder, rivet, bolts,screws, etc.).

The vent block is generally designed to create a pressure drop as thematerial enters the vent cavity. The pressure drop is used to facilitatein inhibiting or preventing material being fed through the vent cavityfrom flowing into the ring gap and the cavity gap. The pressure drop inthe cavity can be accomplished in one or more ways. As illustrated inFIG. 3, the front portion of the vent cavity has a cross-sectional sizethat is greater than the cross-sectional size of the feed flange 138.The larger cross-sectional size or area of the vent cavity results inthe screw element being starved of material when the material is fedinto the vent cavity. Because the front end 310 of screw element 300 isstarved of material, the material more readily is fed forward of thering gap and cavity gap thereby limiting or preventing material fromplugging the ring gap and vent gap. As can be appreciated, the pressuredrop in the front portion of the vent cavity can be accomplished isother or additional ways. For example, the cross-sectional size or areaof the root portion of the screw element can be reduced at the frontportion or all of the screw element to cause the material entering thevent cavity to be starved in the front section of the vent cavity. Also,the pitch of the flights 330 on the screw cavity can be changed to causethe front portion of the screw element to be starved with materialentering the vent cavity, thus resulting in a pressure drop in at leastthe front portion of the vent cavity. One, two or all three of theseconfigurations for the vent cavity and screw element can be used toachieve the pressure drop in at least the front portion of the ventcavity. As illustrated in FIG. 5, the vent cavity has a generallyuniform cross-sectional shape and cross-sectional size or area along thecomplete longitudinal length of the vent cavity. For such a vent cavityconfiguration, the reduction in cross-sectional size or area of the rootportion of the screw element and/or change in the pitch of the flightsin the screw element can be used to achieve the pressure drop in atleast the front portion of the vent cavity. Once the material in thevent cavity has been fed past the ring gap and cavity gap, the ventcavity and/or the screw element can be designed such that the screwelement is not starved of material; however, this is not required. Asillustrated in FIG. 3, the rear or back end of the vent cavity reducesin cross-sectional size or area, thereby causing the screw element insuch region of the vent cavity to be less starved or not starved ofmaterial; however, this is not required. As can be appreciated, the ventcavity can be designed to a plurality of screw elements; however, thisis not required.

The screw element can be designed to include one or more fingers 340that are used to inhibit or prevent material from moving into and/orclogging the ring gap and/or cavity gap. The inclusion of one or morefingers on the screw element is optional. As illustrated in FIG. 4, thefront end 310 of the screw element 300 includes four fingers 340. As canbe appreciated, the screw element can include one, two, three, four ormore fingers. The fingers are illustrated as connected to and extendingfrom the flight 330 of the screw element. The fingers are sized andconfigured to fit at least partially in the ring gap 192 as illustratedin FIG. 3. As the screw element rotates as indicated by the arrow inFIG. 3, the fingers move within the ring gap and clear any material thatmay move into the ring gap. The constant clearing of material from thering gap by the one or more fingers on the screw element facilitate inensuring that the ring gap and cavity gap do not become clogged orplugged during the operation of the extruder arrangement. As illustratedin FIG. 3, the end portion of the fingers extends the full length of theoverlapped region of the inner feed ring and outer ring; however, if canbe appreciated that the end portion of the fingers extends only part ofthe full length of the overlapped region of the inner feed ring andouter ring. The width of the end portion of the fingers is generallyless than the width of the ring gap (e.g., 50-99% the width, etc.) onthat the fingers can easily and/or freely move within the ring gap;however, this is not required. The end portion of the fingers isillustrated in FIG. 3 as spaced from the inner feed ring; however, thisis not required. The end portion of the fingers 340 can include atapered region 342 that designed to facilitate in the movement of thematerial out of the ring gap. The inclusion of a taper region on one ormore of the fingers is optional.

Referring now to FIGS. 1-3 and 5, a second auger 400 is connected to theexit wall of the vent block. The general configuration of the secondauger can be the same as the first auger; however, this is not required.The second auger includes a central root portion 402 and one or moreflights 404 connected to the outside surface of the root portion. Theflight 404 has a helical configuration and is designed to move materialfrom the vent block. The second auger is connected to the second end ofthe screw element so that the first auger, screw element and secondauger rotate together. The diameter of the root portion of the secondauger is non-limiting. The diameter or the root portion can remainconstant or vary along the longitudinal length of the second auger. Theheight and/or pitch of the one or more flights on the second auger canremain constant or vary along the longitudinal length of the secondauger. The second auger can include one or more flight breaks along thelongitudinal length of the second auger; however, this is not required.

A second barrel liner 440 can be formed of one or more parts. Typically,the second barrel liner is formed of two halves that are bolted orotherwise connected together. The material used to form the secondbarrel liner is non-limiting. The second barrel liner includes a firstflange 442 that is connected by bolts 444 or some other or additionalconnection arrangement (e.g., threaded connection, rivet, adhesive,etc.) to the exit wall of the vent block. Although not shown, the secondbarrel liner can optionally include a heating and/or cooling jacketand/or coils to heat and/or cool the material moving though the secondbarrel liner. The cross-sectional size and cross-sectional shape of thecavity 446 formed by the second barrel liner can be constant or varyalong the longitudinal length of the second barrel liner. Thelongitudinal length of the second barrel liner is non-limiting. Thesecond barrel liner can be designed to enable two or more augers torotate within the cavity of the second barrel liner; however, this isnot required. As illustrated in FIG. 1, the cross-sectional size andcircular cross-sectional shape of the cavity formed by the second barrelliner is generally constant along the longitudinal length of the firstbarrel liner. Referring now to FIGS. 1-3, a first flange 442 on thefirst barrel liner is connected to the vent block 100 by bolts or someother or additional connection arrangement. The body of bolt 444 passesthrough a bolt opening 448 and secures to first flange to the exit wallof the vent block. As can be appreciated, other or additionalarrangements can be used to secure the second barrel liner to the ventblock. A third barrel liner 450 is illustrated in FIG. 1 to be connectedto the second barrel liner; however, this is not required. As can beappreciated, additional barrel liners can be connected together in theextruder arrangement. A flange 449 of the second barrel liner isconnected to a flange 452 of the third barrel liner by bolts 460.Although not shown, a die plate can be connected to the end of the thirdbarrel liner; however, this is not required. As also can be appreciated,a third auger, not shown, can be connected to the second auger.

The cross-sectional shape and cross-sectional size or area of the cavityof the second barrel is generally the same as the opening 188 in theexit wall 180 of the vent block; however, this is not required. Thecross-sectional shape and cross-sectional size or area of the opening inthe inner feed ring is also generally the same as the opening 188 in theexit wall 180 of the vent block; however, this is not required. Thesecond end portion 350 of the screw element can be tapered; however,this is not required. The second end portion of the screw element can beconfigured to be connected to the second auger in a similar manner asthe first end portion of the screw element is connected to the firstauger; however, this is not required. The first end portion 410 of thesecond auger 400 is illustrated as tapered to transition from the largercross-sectional size of the root section of the screw element to thesmall cross-sectional size of the root element on the second auger;however, the use of a tapered section is not required. As can beappreciated, the cross-sectional size of the root section of the screwelement can be the same or greater than the cross-sectional size of theroot section of the screw element. A sealing ring 470 can optionally beused to create a seal between the second barrel and the vent block;however, this is not required.

Referring again to FIG. 1, the vent block includes first and second sidewalls 280, 290. One or both side walls can be designed to be hingedlyconnected to the vent block; however, this is not required. Asillustrated in FIG. 1, a screw or bolt 282 is used to secure the sidewall in the closed position. As can be appreciated, other or additionalarrangements can be used to secure the one or both side walls in theclosed position (e.g., latch, lock, rivet, screw, adhesive, weld bead,solder, magnet, etc.). A sealing arrangement (e.g., sealing ring, etc.)can be used to facilitate in forming a seal with the side walls and/orone or more of the other walls of the vent block to facilitate ismaintaining a vacuum in the vent block; however, this is not required.One or both side walls can include a viewing panel 284 to enable a userto view the interior of the vent block; however, this is not required.The viewing panel, when used, enables a user to see if the ring gapand/or cavity gap have become plugged with material. If one or both gapshave become plugged, one or both side walls can be opened and one orboth gaps can be cleared by a user. The vent block can also oralternatively include and/or be used with one or more pressure sensorsthat can be used to determine if the ring gap and/or cavity gap havebecome partially or fully clogged or plugged; however, this is notrequired.

It will thus be seen that the objects set forth above, among those madeapparent from the preceding description, are efficiently attained, andsince certain changes may be made in the constructions set forth withoutdeparting from the spirit and scope of the invention, it is intendedthat all matter contained in the above description and shown in theaccompanying drawings shall be interpreted as illustrative and not in alimiting sense. The invention has been described with reference topreferred and alternate embodiments. Modifications and alterations willbecome apparent to those skilled in the art upon reading andunderstanding the detailed discussion of the invention provided herein.This invention is intended to include all such modifications andalterations insofar as they come within the scope of the presentinvention. It is also to be understood that the following claims areintended to cover all of the generic and specific features of theinvention herein described and all statements of the scope of theinvention, which, as a matter of language, might be said to falltherebetween. The invention has been described with reference to thepreferred embodiments. These and other modifications of the preferredembodiments as well as other embodiments of the invention will beobvious from the disclosure herein, whereby the foregoing descriptivematter is to be interpreted merely as illustrative of the invention andnot as a limitation. It is intended to include all such modificationsand alterations insofar as they come within the scope of the appendedclaims.

I claim:
 1. A method for removing gas from material fed through anextruder, said method comprising: providing a material; providing anextruder; feeding said material into an entrance of said extruder;providing a first auger rotatably positioned in a first barrel;providing a second auger rotatably positioned in a second barrel;providing a vent block, said vent block including a vent cavity having afeed end and an exit end, an inner feed ring that partially extends intosaid vent cavity at said feed end of said vent cavity, and a screwelement rotatably positioned in said vent cavity, a first end of saidscrew element connected to or interconnected to said first auger, asecond end of said screw element connected to or interconnected to saidsecond auger, at least a majority of said vent cavity formed by an outerring, a front portion of said outer ring having a cross-sectional sizethat is greater than a cross-sectional size of a front end of said innerfeed ring, at least a portion of a front end of said outer ring islongitudinally aligned with or overlapping said front end of said innerfeed ring, said outer ring forming at least one gap or opening at oradjacent said feed end of said vent cavity; rotating said first auger tocause said material to be fed from said entrance of said extruder tosaid vent block; and, creating a vacuum on said vent block to cause avacuum to be pulled on said vent cavity as said material is moved thoughsaid vent cavity from said feed end to said exit end by said screwelement.
 2. The method as defined in claim 1, wherein said vent cavity,said screw element, or combinations thereof are configured to cause saidvent cavity to be at least partially starved of material as saidmaterial is passed though said vent cavity.
 3. The method as defined inclaim 2, wherein said front end of said outer ring overlaps said frontend of said inner feed ring, said front end of said outer ring spacedfrom said feed end of said cavity to form said at least one gap.
 4. Themethod as defined in claim 1, wherein said front end of said outer ringoverlaps said front end of said inner feed ring, said front end of saidouter ring spaced from said feed end of said cavity to form said atleast one gap.
 5. The method as defined in claim 4, including a viewingwindow on a vent block wall, and including the step of looking into saidviewing window to determine whether material has plugged a space definedby said front portion of said outer ring overlapping said inner feedring.
 6. The method as defined in claim 1, wherein said screw elementincludes a root portion that extends along the longitudinal length ofthe screw element and a helically shaped flight connected to an outersurface of said root portion, a cross-sectional area of said rootportion at said first end of said screw element is greater than saidcross-sectional area of said root portion at said second end of saidscrew element.
 7. The method as defined in claim 1, wherein said screwelement includes a root portion that extends along the longitudinallength of the screw element, a helically shaped flight connected to anouter surface of said root portion and a finger, said finger positionedat or adjacent to said first end of said screw element, said fingerconfigured to be positioned in said at least one gap or opening, andincluding the step of said finger at least partially clearing said atleast one gap or opening of said material as said screw element isrotated in said vent cavity.
 8. The method as defined in claim 1,wherein said front end of said outer ring overlaps said front end ofsaid inner feed ring, said front end of said outer ring spaced from saidfeed end of said cavity to form said at least one gap.
 9. The method asdefined in claim 8, wherein said screw element includes a root portionthat extends along the longitudinal length of the screw element and ahelically shaped flight connected to an outer surface of said rootportion, a height of said flight at said first end of said screw elementis greater than a height of said flight at said second end of said screwelement.
 10. The method as defined in claim 9, wherein said screwelement includes a finger, said finger positioned at or adjacent to saidfirst end of said screw element, said finger configured to be positionedin said at least one gap or opening, and including the step of saidfinger at least partially clearing said at least one gap or opening ofsaid material as said screw element is rotated in said vent cavity. 11.The method as defined in claim 10, including a viewing window on a ventblock wall, and including the step of looking into said viewing windowto determine whether material has plugged a space defined by said frontportion of said outer ring overlapping said inner feed ring.
 12. Themethod as defined in claim 11, wherein said outer ring having a variablecross-sectional area along a longitudinal length of said outer ring. 13.The method as defined in claim 1, wherein said outer ring having avariable cross-sectional area along a longitudinal length of said outerring.
 14. A method for removing gas from material fed through anextruder, said method comprising: providing a material; providing anextruder; feeding said material into an entrance of said extruder;providing a first auger rotatably positioned in a first barrel;providing a second auger rotatably positioned in a second barrel;providing a vent block, said vent block including a vent cavity having afeed end and an exit end, an inner feed ring, an outer ring and a screwelement, said inner feed ring partially extends into said vent cavity atsaid feed end of said vent cavity, said screw element rotatablypositioned in said vent cavity, a first end of said screw elementconnected to or interconnected to said first auger, a second end of saidscrew element connected to or interconnected to said second auger, afront portion of said outer ring having a cross-sectional size that isgreater than a cross-sectional size of a front end of said inner feedring, at least a portion of a front end of said outer ring islongitudinally aligned with or overlapping said front end of said innerfeed ring, said outer ring and said inner feed ring forming at least onegap or opening; rotating said first auger to cause said material to befed from said entrance of said extruder to said vent block; and,creating a vacuum on said vent block to cause a vacuum to be pulled onsaid vent cavity as said material is moved though said vent cavity fromsaid feed end to said exit end by said screw element.
 15. The method asdefined in claim 14, wherein said front end of said outer ring overlapsat least a portion of said front end of said inner feed ring, said frontend of said outer ring spaced from said feed end of said cavity.
 16. Themethod as defined in claim 15, wherein at least a majority of said ventcavity is formed by an outer ring.
 17. The method as defined in claim16, wherein said vent cavity, said screw element, or combinationsthereof are configured to cause said vent cavity to be at leastpartially starved of material as said material is passed though saidvent cavity, said outer ring having a variable cross-sectional areaalong a longitudinal length of said outer ring.
 18. The method asdefined in claim 17, wherein said screw element includes a root portionthat extends along the longitudinal length of the screw element and ahelically shaped flight connected to an outer surface of said rootportion, a height of said flight at said first end of said screw elementgreater than a height of said flight at said second end of said screwelement.
 19. The method as defined in claim 18, wherein said screwelement includes a finger, said finger positioned at or adjacent to saidfirst end of said screw element, said finger configured to be positionedin said at least one gap or opening, and including the step of saidfinger at least partially clearing said at least one gap or opening ofsaid material as said screw element is rotated in said vent cavity. 20.The method as defined in claim 19, including a viewing window on a ventblock wall, and including the step of looking into said viewing windowto determine whether material has plugged a space defined by said frontportion of said outer ring overlapping said inner feed ring.